It looks like Bush may actually be picking up a point or two after the debate. Some of this may be due to Republicans just being relieved by Bush finally putting in a competent performance. But it may be also due to Republicans hyping Kerry's mention of Mary Cheney.
A few thoughts on this:
1. Unlike journalists and political junkies, many voters may have been unaware that Mary is gay until Kerry mentioned it. They may have thought that Kerry was "outing" her when he was doing nothing of the kind.
2. Homosexuality is still an uncomfortable issue for many voters, particularly older people. Especially when it involves someone's children. (How many voters know that Mary is in her thirties, and hardly a "child" in any but the biological sense?) They may be annoyed by Kerry's bringing it up and forcing them to think about it. (But even unbigoted voters may have found Kerry's statement just kinda weird and out of place. I know I did).
3. Republicans are successfully spinning this not as a gay issue, but as a "Kerry will say anything" issue and as a violation of family privacy. (Although, once again, Mary's hardly private about her sexuality).